U.S. patent application number 15/840199 was filed with the patent office on 2018-06-21 for optical module and optical transmission equipment.
The applicant listed for this patent is Oclaro Japan, Inc.. Invention is credited to Daisuke NOGUCHI.
Application Number | 20180172933 15/840199 |
Document ID | / |
Family ID | 62562394 |
Filed Date | 2018-06-21 |
United States Patent
Application |
20180172933 |
Kind Code |
A1 |
NOGUCHI; Daisuke |
June 21, 2018 |
OPTICAL MODULE AND OPTICAL TRANSMISSION EQUIPMENT
Abstract
There is provided an optical module, including a first optical
subassembly, a second optical subassembly, a first flexible printed
circuit board, and a second flexible printed circuit board. The
first/second optical subassembly includes a first/second normal
phase lead terminal and a first/second reverse phase lead terminal,
arranged in a positive direction of a first orientation. The
first/second flexible printed circuit board includes a first/second
normal phase strip conductor, a first/second reverse phase strip
conductor, and a ground conductor layer. The back surface of the
first/second flexible printed circuit board faces the end surface
of the first/second optical subassembly. The first/second normal
phase strip conductor extends in a positive/negative direction of a
second orientation.
Inventors: |
NOGUCHI; Daisuke;
(Sagamihara, Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Oclaro Japan, Inc. |
Sagamihara |
|
JP |
|
|
Family ID: |
62562394 |
Appl. No.: |
15/840199 |
Filed: |
December 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4215 20130101;
H05K 1/118 20130101; G02B 6/4203 20130101; H05K 1/147 20130101;
H04B 10/40 20130101; H05K 3/103 20130101; G02B 6/4281 20130101;
H05K 1/148 20130101; H05K 2201/10121 20130101 |
International
Class: |
G02B 6/42 20060101
G02B006/42; H05K 1/14 20060101 H05K001/14; H04B 10/40 20060101
H04B010/40; H05K 1/11 20060101 H05K001/11; H05K 3/10 20060101
H05K003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2016 |
JP |
2016-246745 |
Claims
1. An optical module comprising: a first optical subassembly,
including a first normal phase lead terminal and a first reverse
phase lead terminal which are disposed on an end surface so as to
be in a row in order in a positive direction of a first
orientation; a second optical subassembly, including a second
normal phase lead terminal and a second reverse phase lead terminal
which are disposed on the end surface so as to be in a row in order
in the positive direction of the first orientation; a first
flexible printed circuit board, including a first normal phase
strip conductor connected to the first normal phase lead terminal,
a first reverse phase strip conductor connected to the first
reverse phase lead terminal, and a ground conductor layer disposed
on a back surface, the first normal phase strip conductor and the
first reverse phase strip conductor being disposed on a front
surface to extend in parallel with each other; a second flexible
printed circuit board, including a second normal phase strip
conductor connected to the second normal phase lead terminal, a
second reverse phase strip conductor connected to the second
reverse phase lead terminal, and a ground conductor layer disposed
on the back surface, the second normal phase strip conductor and
the second reverse phase strip conductor being disposed on the
front surface to extend in parallel with each other; a printed
circuit board, including a first surface and a second surface; and
an IC, being mounted on any one of the first surface and the second
surface of the printed circuit board, and is electrically connected
to the first optical subassembly and the second optical subassembly
together, wherein the first flexible printed circuit board is
connected to the first optical subassembly so as to cause the back
surface of the first flexible printed circuit board to face the end
surface of the first optical subassembly, wherein the second
flexible printed circuit board is connected to the second optical
subassembly so as to cause the back surface of the second flexible
printed circuit board to face the end surface of the second optical
subassembly, wherein the first normal phase strip conductor and the
first reverse phase strip conductor of the first flexible printed
circuit board extend at a connection portion with the end surface
of the first optical subassembly in a positive direction of a
second orientation which intersects with the first orientation, and
wherein the second normal phase strip conductor and the second
reverse phase strip conductor of the second flexible printed
circuit board extend at a connection portion with the end surface
of the second optical subassembly in a negative direction of the
second orientation.
2. The optical module according to claim 1, wherein a normal
orientation of the first surface of the printed circuit board and a
normal orientation of the second surface thereof are directed in
the second orientation together, wherein the printed circuit board
further includes a first normal phase board terminal connected to
the first normal phase strip conductor and a first reverse phase
board terminal connected to the first reverse phase strip
conductor, the first normal phase board terminal and the first
reverse phase board terminal being disposed on the first surface in
a row in order in the positive direction of the first orientation,
and wherein the printed circuit board further includes a second
normal phase board terminal connected to the second normal phase
strip conductor and a second reverse phase board terminal connected
to the second reverse phase strip conductor, the second normal
phase board terminal and the second reverse phase board terminal
being disposed on the second surface in a row in order in the
positive direction of the first orientation.
3. The optical module according to claim 2, wherein the first
surface of the printed circuit board rather than the second surface
is disposed on a positive side of the second orientation, wherein
the first flexible printed circuit board is connected to cause the
front surface to face the first surface, and wherein the second
flexible printed circuit board is connected to cause the front
surface to face the second surface.
4. The optical module according to claim 2, wherein the first
surface of the printed circuit board rather than the second surface
is disposed on a negative side of the second orientation, wherein
the first flexible printed circuit board is connected to cause the
back surface to face the first surface, and wherein the second
flexible printed circuit board is connected to cause the back
surface to face the second surface.
5. The optical module according to claim 1, wherein the first
optical subassembly and the second optical subassembly are disposed
in a row in the second orientation.
6. The optical module according to claim 3, wherein the first
optical subassembly and the second optical subassembly are disposed
in a row in order in the negative direction of the second
orientation.
7. The optical module according to claim 4, wherein the first
optical subassembly and the second optical subassembly are disposed
in a row in order in the positive direction of the second
orientation.
8. The optical module according to claim 5, wherein the printed
circuit board further comprises: a first differential transmission
line connected to the first normal phase board terminal and the
first reverse phase board terminal; and a second differential
transmission line connected to the second normal phase board
terminal and the second reverse phase board terminal, wherein the
IC includes a first normal phase IC terminal and a first reverse
phase IC terminal which are disposed in a row in order in a
positive direction of a third orientation, and includes a second
normal phase IC terminal and a second reverse phase IC terminal
which are disposed in a row in order in the positive direction of
the third orientation, wherein the IC is mounted on the first
surface of the printed circuit board, wherein the first
differential transmission line extends from the first normal phase
board terminal and the first reverse phase board terminal on the
first surface, so as to be connected to the first normal phase IC
terminal and the first reverse phase IC terminal, and wherein the
second differential transmission line extends from the second
normal phase board terminal and the second reverse phase board
terminal on the second surface, extends from the second surface to
the first surface in a stacking direction, and then extends on the
first surface so as to be connected to the second normal phase IC
terminal and the second reverse phase IC terminal.
9. The optical module according to claim 8, wherein the positive
direction of the third orientation corresponds to the positive
direction of the first orientation.
10. The optical module according to claim 1, wherein the first
flexible printed circuit board and the second flexible printed
circuit board have a common structure.
11. The optical module according to claim 1, wherein the first
optical subassembly and the second optical subassembly have a
common structure except that each of the first optical subassembly
and the second optical subassembly includes a light-emitting
element configured to emit an optical signal of a different
wavelength.
12. An optical transmission equipment in which the optical module
according to claim 1 is mounted.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority from Japanese
application JP 2016-246745, filed on Dec. 20, 2016, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to an optical module and
optical transmission equipment, particularly to a technology in
which a plurality of optical subassemblies are mounted in an
optical module with a simple configuration.
2. Description of the Related Art
[0003] Recently, a request of reduction in size and cost of an
optical module capable of dense transmission has been risen. A
technology of transmitting a large capacity signal, which is
referred to as wavelength division multiplexing (WDM) is used for
dense transmission. In the WDM, a wavelength division multiplexed
optical signal is generated by performing multiplexing of a
plurality of optical signals having wavelengths different from each
other, or a plurality of optical signals having wavelengths
different from each other are generated by performing
de-multiplexing of a wavelength division multiplexed optical
signal.
[0004] In a case where the optical module is an optical transmitter
module, or in a case where the optical module includes an optical
transmitter module, the optical transmitter module includes a
plurality of light-emitting elements that emit optical signals
having wavelengths different from each other. In a case where the
optical module is an optical receiver module, or in a case where
the optical module includes an optical receiver module, the optical
receiver module includes a plurality of light-receiving elements
that receive optical signals having wavelengths different from each
other. In the related art, a light-emitting element array in which
a plurality of light-emitting elements are integrated with each
other, or a light-receiving element array in which a plurality of
light-receiving elements are integrated with each other is used.
The array type includes a form in which each of elements is mounted
on one submount, in addition to a form in which a plurality of
elements are integrated with each other on a single substrate. JP
2016-178218 A discloses a structure of an optical module including
an array type light-emitting element.
SUMMARY OF THE INVENTION
[0005] However, in an optical element array such as a
light-emitting element array or a light-receiving element array, in
which a plurality of optical elements are integrate, in a case
where even one of the plurality of optical elements included in the
optical element array does not satisfy the standard condition, the
optical element array itself does not satisfy the standard
condition. Thus, yield is deteriorated, and manufacturing cost is
increased. In addition, for example, in an optical element array in
which a plurality of optical elements are monolithically integrated
on the same semiconductor substrate, manufacturing cost is
increased because, for example, an active layer of each of the
optical element is formed in an individual process.
[0006] In order to preferentially achieve reduction of cost, an
optical module in which a plurality of optical subassemblies are
mounted is desired. Here, each of the plurality of optical
subassemblies includes one light conversion element configured to
emit an optical signal having a different wavelength or receive
light having a different wavelength. However, if a plurality of
optical subassemblies are mounted in an optical module, a space for
the plurality of optical subassemblies is required, and thus it is
difficult to reduce the size of the optical module.
[0007] In order to realize reduction in size, it is considered that
a plurality of optical subassemblies are arranged
three-dimensionally rather than planarly. In this case, for space
constraints, it is desired that some of the optical subassemblies
are connected to a group of terminals disposed on the front surface
of a printed circuit board and others are connected to a group of
terminals disposed on the back surface of the printed circuit
board. In order to realize reduction of cost, the plurality of
optical subassemblies may be controlled by a common IC. For this,
any of, for example, methods; a method in which groups of terminals
of the IC are specially arranged; a method in which a transmission
line of the printed circuit board is set to have a special
structure; and a method in which a transmission line of a flexible
printed circuit board, which connects the optical subassemblies and
the printed circuit board is set to have a special structure is
required. Thus, this acts as a factor of hindering reduction in
size and cost.
[0008] Considering the above problems, an object of the present
invention is to provide an optical module and optical transmission
equipment which are realized with a simple configuration, and
include a plurality of optical subassemblies mounted therein.
[0009] (1) To solve the above problems, according to the present
invention, an optical module includes a first optical subassembly,
a second optical subassembly, a first flexible printed circuit
board, a second flexible printed circuit board, a printed circuit
board, and an IC. The first optical subassembly includes a first
normal phase lead terminal and a first reverse phase lead terminal
which are disposed on an end surface so as to be in a row in order
in a positive direction of a first orientation. The second optical
subassembly includes a second normal phase lead terminal and a
second reverse phase lead terminal which are disposed on the end
surface so as to be in a row in order in the positive direction of
the first orientation. The first flexible printed circuit board
includes a first normal phase strip conductor connected to the
first normal phase lead terminal, a first reverse phase strip
conductor connected to the first reverse phase lead terminal, and a
ground conductor layer disposed on a back surface. The first normal
phase strip conductor and the first reverse phase strip conductor
are disposed on a front surface to extend in parallel with each
other. The second flexible printed circuit board includes a second
normal phase strip conductor connected to the second normal phase
lead terminal, a second reverse phase strip conductor connected to
the second reverse phase lead terminal, and a ground conductor
layer disposed on the back surface. The second normal phase strip
conductor and the second reverse phase strip conductor are disposed
on the front surface to extend in parallel with each other. The
printed circuit board includes a first surface and a second
surface. The IC is mounted on any one of the first surface and the
second surface of the printed circuit board, and is electrically
connected to the first optical subassembly and the second optical
subassembly together. The first flexible printed circuit board is
connected to the first optical subassembly so as to cause the back
surface of the first flexible printed circuit board to face the end
surface of the first optical subassembly. The second flexible
printed circuit board is connected to the second optical
subassembly so as to cause the back surface of the second flexible
printed circuit board to face the end surface of the second optical
subassembly. The first normal phase strip conductor and the first
reverse phase strip conductor of the first flexible printed circuit
board extend at a connection portion with the end surface of the
first optical subassembly in a positive direction of a second
orientation which intersects with the first orientation. The second
normal phase strip conductor and the second reverse phase strip
conductor of the second flexible printed circuit board extend at a
connection portion with the end surface of the second optical
subassembly in a negative direction of the second orientation.
[0010] (2) In the optical module described in (1), a normal
orientation of the first surface of the printed circuit board and a
normal orientation of the second surface thereof may be directed in
the second orientation together. The printed circuit board may
further include a first normal phase board terminal connected to
the first normal phase strip conductor and a first reverse phase
board terminal connected to the first reverse phase strip
conductor. The first normal phase board terminal and the first
reverse phase board terminal may be disposed on the first surface
in a row in order in the positive direction of the first
orientation. The printed circuit board may further include a second
normal phase board terminal connected to the second normal phase
strip conductor and a second reverse phase board terminal connected
to the second reverse phase strip conductor. The second normal
phase board terminal and the second reverse phase board terminal
may be disposed on the second surface in a row in order in the
positive direction of the first orientation.
[0011] (3) In the optical module described in (2), the first
surface of the printed circuit board rather than the second surface
may be disposed on a positive side of the second orientation. The
first flexible printed circuit board may be connected to cause the
front surface to face the first surface. The second flexible
printed circuit board may be connected to cause the front surface
to face the second surface.
[0012] (4) In the optical module described in (2), the first
surface of the printed circuit board rather than the second surface
may be disposed on a negative side of the second orientation. The
first flexible printed circuit board may be connected to cause the
back surface to face the first surface. The second flexible printed
circuit board may be connected to cause the back surface to face
the second surface.
[0013] (5) In the optical module described in any of (1) to (4),
the first optical subassembly and the second optical subassembly
may be disposed in a row in the second orientation.
[0014] (6) In the optical module described in (3), the first
optical subassembly and the second optical subassembly may be
disposed in a row in order in the negative direction of the second
orientation.
[0015] (7) In the optical module described in (4), the first
optical subassembly and the second optical subassembly may be
disposed in a row in order in the positive direction of the second
orientation.
[0016] (8) In the optical module described in (5), the printed
circuit board may further include: a first differential
transmission line connected to the first normal phase board
terminal and the first reverse phase board terminal; and a second
differential transmission line connected to the second normal phase
board terminal and the second reverse phase board terminal. The IC
may include a first normal phase IC terminal and a first reverse
phase IC terminal which are disposed in a row in order in a
positive direction of a third orientation, and include a second
normal phase IC terminal and a second reverse phase IC terminal
which are disposed in a row in order in the positive direction of
the third orientation. The IC may be mounted on the first surface
of the printed circuit board. The first differential transmission
line may extend from the first normal phase board terminal and the
first reverse phase board terminal on the first surface, so as to
be connected to the first normal phase IC terminal and the first
reverse phase IC terminal. The second differential transmission
line may extend from the second normal phase board terminal and the
second reverse phase board terminal on the second surface, extend
from the second surface to the first surface in a stacking
direction, and then extend on the first surface so as to be
connected to the second normal phase IC terminal and the second
reverse phase IC terminal.
[0017] (9) In the optical module described in (8), the positive
direction of the third orientation may correspond to the positive
direction of the first orientation.
[0018] (10) In the optical module described in any of (1) to (9),
the first flexible printed circuit board and the second flexible
printed circuit board may have a common structure.
[0019] (11) In the optical module described in any of (1) to (10),
the first optical subassembly and the second optical subassembly
may have a common structure except that each of the first optical
subassembly and the second optical subassembly includes a
light-emitting element configured to emit an optical signal of a
different wavelength.
[0020] (12) According to the present invention, optical
transmission equipment may include the optical module which is
described in any of (1) to (11) and is mounted therein.
[0021] According to the present invention, there are provided an
optical module and optical transmission equipment which are
realized with a simple configuration, and include a plurality of
optical subassemblies mounted therein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic diagram illustrating a configuration
of optical transmission equipment and an optical module according
to a first embodiment of the present invention.
[0023] FIG. 2 is a perspective view schematically illustrating a
configuration of an optical transmitter section according to the
first embodiment of the present invention.
[0024] FIG. 3 is a perspective view schematically illustrating a
configuration of the optical transmitter section according to the
first embodiment of the present invention.
[0025] FIG. 4 is a cross-sectional view schematically illustrating
a configuration of an LD module according to the first embodiment
of the present invention.
[0026] FIG. 5A is a perspective view schematically illustrating a
configuration of the optical module according to the first
embodiment of the present invention.
[0027] FIG. 5B is a perspective view schematically illustrating the
configuration of the optical module according to the first
embodiment of the present invention.
[0028] FIG. 6 is a diagram illustrating a connection relationship
between two LD modules and two flexible printed circuit boards
according to the first embodiment of the present invention.
[0029] FIG. 7A is a plan view illustrating an end portion of the
flexible printed circuit board according to the first embodiment of
the present invention.
[0030] FIG. 7B is a bottom view illustrating the end portion of the
flexible printed circuit board according to the first embodiment of
the present invention.
[0031] FIG. 8 is a plan view illustrating an end portion of a
printed circuit board according to the first embodiment of the
present invention.
[0032] FIG. 9 is a plan view illustrating the printed circuit board
according to the first embodiment of the present invention.
[0033] FIG. 10 is a cross-sectional view illustrating the printed
circuit board according to the first embodiment of the present
invention.
[0034] FIG. 11 is a cross-sectional view illustrating an optical
module according to a second embodiment of the present
invention.
[0035] FIG. 12 is a diagram illustrating a connection relationship
between two LD modules and two flexible printed circuit boards
according to the second embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] Hereinafter, embodiments of the present invention will be
specifically described in detail with reference to the drawings. In
all of the drawings for describing the embodiments, members having
the same function are denoted by the same reference signs and
repetitive descriptions thereof will be omitted. The drawings which
will be illustrated below are just used for describing examples of
the embodiments. The size of constituent components in the drawings
and the scale which will be described in the examples do not
necessarily coincide with each other.
First Embodiment
[0037] FIG. 1 is a schematic diagram illustrating a configuration
of optical transmission equipment 1 and an optical module 2
according to a first embodiment of the present invention. The
optical transmission equipment 1 includes a printed circuit board
11 and an IC 12. A plurality of optical modules 2 are mounted on
the optical transmission equipment 1 by electric ports 5,
respectively. The optical transmission equipment 1 is, for example,
a router or a switch of high capacity. For example, the optical
transmission equipment 1 has a function of a switch board, and thus
is disposed in a base station or the like. The optical transmission
equipment 1 acquires reception data (receiving electric signal) by
the optical module 2. The optical transmission equipment 1
determines data to be transmitted and a transmission destination,
generates transmission data (transmitting electric signal), and
transfers the generated data to the corresponding optical module 2,
by using the IC 12 and the like which are mounted in the printed
circuit board 11.
[0038] The optical module 2 is a transceiver which has a function
of optical transmitting and a function of optical receiving. The
optical module 2 includes a printed circuit board 21, flexible
printed circuit boards 22A and 22B, an optical transmitter section
23A, and an optical receiver section 23B. The optical transmitter
section 23A converts electric signals into optical signals and
transmits the optical signals to an optical fiber 3A. The optical
receiver section 23B converts optical signals received via an
optical fiber 3B into electric signals. The printed circuit board
21 and the optical transmitter section 23A are connected to each
other via the flexible printed circuit board 22A. The printed
circuit board 21 and the optical receiver section 23B are connected
to each other via the flexible printed circuit board 22B. Electric
signals are transmitted to the optical transmitter section 23A via
the flexible printed circuit board 22A by the printed circuit board
21. Electric signals are transmitted to the printed circuit board
21 via the flexible printed circuit board 22B by the optical
receiver section 23B. A light conversion element is an element
configured to convert an optical signal into an electric signal or
to convert an electric signal into an optical signal. A light
conversion element that converts an electric signal into an optical
signal functions as a light-emitting element, and a light
conversion element that converts an optical signal into an electric
signal functions as a light-receiving element. The optical
transmitter section 23A includes one or a plurality (here, four) of
light-emitting elements. The optical receiver section 23B includes
one or a plurality (here, four) of light-receiving elements.
[0039] A transmission system according to the embodiment includes
two or more optical transmission equipments 1, two or more optical
modules 2, and one or more optical fibers 3. One or more optical
modules 2 are mounted on each of the two or more optical
transmission equipments 1. The optical modules 2 which are
respectively mounted on the two optical transmission equipments 1
are connected to each other by the optical fiber 3 (for example,
optical fiber 3A). Transmission data generated by one of the two
optical transmission equipments 1 is converted into an optical
signal by the optical module 2 mounted therein, and the optical
signal is transmitted to the optical fiber 3. The optical signal
transmitted on the optical fiber 3 is received by the optical
module 2 mounted on the other of the two optical transmission
equipments 1. The optical module 2 converts the optical signal into
an electric signal and transmits the electric signal to the other
of the two optical transmission equipment 1 as reception data.
[0040] The optical transmission equipment 1 and the optical module
2 according to the embodiment correspond to high speed optical
fiber transmission of a bit rate which is about 100 Gbit/s, and
satisfy the request for distribution and speed-up of a broadband
network with an increase of communication traffic in the recent
years. The optical module 2 according to the embodiment is an
optical transceiver which satisfies the request for reduction in
size and cost. Nowadays, for the optical transceiver (optical
module), Multi Source Agreement (MSA) between a plurality of
manufacturers is signed, and thus commercialization in a state
where electric characteristics, optical characteristics, external
dimensions, and the like are set based on the same standards is in
progress. The MSA based on the Ethernet (Registered Trademark)
leads. Regarding the external dimensions of an optical module, for
example, the standards of a CFP2, a CFP4, a QSFP28 having a size
which is obtained by reducing the external size of a 100 Gbit/s
optical communication module CFP (100 Gigabit Form Factor
Pluggable) or a 100 Gbit/s optical communication module CFP are
provided. The position of an optical transmission receptacle, an
optical reception receptacle, or an electric interface card edge is
determined based on the above standards. It is considered that the
flow of standardization and reduction in size as described above
continue.
[0041] The optical module 2 according to the embodiment is, for
example, based on the MSA standards of the QSFP28 and the CFP4.
Reduction of a case volume and a decrease of the number of
components are in progress based on the standards. A transmission
system based on the standards is a wavelength division multiplexing
(WDM) transmission system for 4 wavelengths. Four light-emitting
elements (for example, semiconductor laser elements) configured to
emit optical signals having wavelengths different from each other
are used in the optical transmitter section 23A. A 4-channel
differential transmission lines for transmitting and a 4-channel
differential transmission lines for receiving are disposed on the
printed circuit board 21 included in the optical module 2. The
specification of an electric signal for serial data is based on OIF
CEI-28G. A bit rate of an electric signal which is transmitted on
each channel has any value in a range of 25 Gbit/s to 28 Gbit/s.
Modulation driving is performed on the four light-emitting elements
for each channel by a driver circuit. As the light-emitting
element, a direct-modulation DFB-LD element (distributed feedback
laser) is suitably used from a viewpoint of reduction in cost. FIG.
2 is a perspective view schematically illustrating a configuration
of the optical transmitter section 23A according to the embodiment.
The optical transmitter section 23A according to the embodiment
includes 4 laser diode (LD) modules 31A, 31B, 31C, and 31D, and an
optical MUX module 32 (multiplexer). Each of the LD module
corresponds to an optical subassembly. The optical MUX module 32
has an optical multiplexing function of the optical transmitter
section 23A, and includes a sleeve assembly 33 for connecting
multiplexed light (wavelength division multiplexed optical signal)
to the external optical fiber 3A. The 4 LD modules 31A, 31B, 31C,
and 31D respectively emit optical signals having wavelengths
different from each other. For example, for the purpose of CWDM,
the 4 LD modules 31A, 31B, 31C, and 31D emit optical signals having
light wavelengths in 4 wavelength bands, that is, a wavelength band
of 1271 nm, a wavelength band of 1291 nm, and a wavelength band of
1311 nm, and a wavelength band of 1331 nm, respectively.
[0042] FIG. 3 is a perspective view schematically illustrating the
configuration of the optical transmitter section 23A according to
the embodiment. FIG. 3 illustrates a state of excluding the LD
modules 31A, 31B, 31C, and 31D from the optical transmitter section
23A illustrated in FIG. 2. The optical MUX module 32 has 4
installation portions 34A, 34B, 34C, and 34D. The 4 installation
portions 34A, 34B, 34C, and 34D come into contact with joint places
to tips (ferrules 38 which will be described later) of the 4 LD
modules 31A, 31B, 31C, and 31D, and thus are jointed to the tips of
the 4 LD modules, respectively. Each of the installation portions
has a function of holding and fixing the LD module. Each of the LD
modules includes a stem 35 on a side of being connected to the
flexible printed circuit board 22A. The stem 35 includes one pair
of lead terminals. A +x direction illustrated in FIGS. 2 and 3
corresponds to a positive direction of a first orientation.
[0043] A +y direction illustrated in FIGS. 2 and 3 corresponds to a
positive direction of a second orientation. The second orientation
corresponds to an orientation which intersects with the first
orientation. Here, the second orientation and the first orientation
are orthogonal.
[0044] FIG. 4 is a cross-sectional view schematically illustrating
a configuration of the LD module 31A according to the embodiment.
Other LD modules 31B, 31C, and 31D also have the same
configuration. Here, the LD module 31A will be described. The LD
module 31A further includes an LD element 36A, a collective lens
37, and a ferrule 38. Each of the LD modules includes one LD
element. A direct-modulation DFB-LD element is used as each LD
element. The LD element 36A corresponds to a light-emitting element
that converts an electric signal into an optical signal. The LD
modules 31B, 31C, and 31D include LD elements 36B, 36C, and 36D,
respectively. The LD elements 36A, 36B, 36C, and 36D have the
common structure except for the different semiconductor multilayer
structures, from a point of emitting optical signals having
wavelengths different from each other. The LD modules 31A, 31B,
31C, and 31D have the common structure except for the LD elements
36A, 36B, 36C, and 36D.
[0045] FIGS. 5A and 5B are perspective diagrams schematically
illustrating the configuration of the optical module 2 according to
the embodiment. FIG. 5A is an external view illustrating the
optical module 2. FIG. 5B illustrates main components mounted in
the optical module 2. As described above, the optical module 2 is
an optical transceiver of a bit rate which is about 100 Gbit/s.
Here, the optical module 2 is based on the MSA standards of the
QSFP28. As illustrated in FIG. 5A, the optical module 2 includes a
case 41, a pulltab 42, a slider 43, and the printed circuit board
21. The main components constitute an appearance of the optical
module 2. The case 41 is formed by molding processing in a manner
that die cast is performed by using metal such as zinc. The slider
43 is formed by sheet metal working with metal such as stainless
steel. The pulltab 42 is formed by injection molding with a
thermoplastic elastomer. The above components are suitably formed
by the above methods, respectively, from a viewpoint of reduction
in cost.
[0046] Then, the main components mounted in the case 41 of the
optical module 2 will be described with reference to FIG. 5B. For
simple descriptions, FIG. 5B does not illustrate the optical MUX
module 32. As illustrated in FIG. 1, the optical module 2 includes
the printed circuit board 21, the flexible printed circuit boards
22A and 22B, the optical transmitter section 23A, and the optical
receiver section 23B. The optical transmitter section 23A includes
the four LD modules 31A, 31B, 31C, and 31D which respectively
correspond to wavelengths. Each of the LD modules corresponds to a
TO-CAN transmitter optical subassembly (TOSA). Practically, the
flexible printed circuit board 22A illustrated in FIG. 1 includes
four flexible printed circuit boards 45A, 45B, 45C, and 45D. The
four flexible printed circuit boards 45A, 45B, 45C, and 45D are
subflexible printed circuit boards for the flexible printed circuit
board 22A. The diameter size of each of the LD modules (TO-CAN
TOSAs) is, here, 3.8 mm. Here, the four LD modules are arranged up
and down in two rows in the optical module 2. The two upper LD
modules 31A and 31D are disposed in a row in order in the +x
direction (positive direction of the first orientation) illustrated
in FIG. 5B. The flexible printed circuit boards 45A and 45D are
connected to the LD modules 31A and 31D so as to cause end surfaces
(connection surface 35A of the stem 35: not illustrated) of the LD
modules 31A and 31D to face back surfaces L2 of the flexible
printed circuit boards 45A and 45D, respectively. The flexible
printed circuit boards 45A and 45D are connected to the printed
circuit board 21 so as to cause front surfaces L1 of the flexible
printed circuit boards 45A and 45D to face a first surface S1
(upper surface) of the printed circuit board 21. The two lower LD
modules 31B and 31C are disposed in a row in order in the +x
direction (positive direction of the first orientation) illustrated
in FIG. 5B. The flexible printed circuit boards 45B and 45C are
connected to the LD modules 31B and 31C so as to cause end surfaces
(connection surface 35A of the stem 35: not illustrated) of the LD
modules 31B and 31C to face the back surfaces L2 of the flexible
printed circuit boards 45B and 45C, respectively. The flexible
printed circuit boards 45B and 45C are connected to the printed
circuit board 21 so as to cause the front surfaces L1 of the
flexible printed circuit boards 45B and 45C to face a second
surface S2 (lower surface) of the printed circuit board 21. With
the above configuration, the components may be mounted in a space
in the case 41 based on the MSA standard of the QSFP28.
[0047] The optical receiver section 23B in the optical module 2
includes a 4-channel receiver optical subassembly (ROSA) 46 in
which four light-receiving elements are mounted. Here, the
light-receiving element corresponds to a photo-diode (PD) element.
The 4-channel ROSA 46 is connected to one end of the flexible
printed circuit board 22B. The other end of the flexible printed
circuit board 22B is connected to the first surface 51 of the
printed circuit board 21.
[0048] As illustrated in FIG. 5B, two ICs 48 and 49 are mounted on
the first surface (upper surface) 51 of the printed circuit board
21. The IC 48 is a driving IC in which a 4-channel CDR circuit for
transmission and a 4-channel driver circuit are integrated. That
is, the IC 48 is electrically connected to the LD modules 31A, 31B,
31C, and 31D. The IC 49 is an IC in which a 4-channel CDR circuit
for receiving is integrated.
[0049] The optical module according to the embodiment includes a
first optical subassembly, a second optical subassembly, a first
flexible printed circuit board, a second flexible printed circuit
board, a printed circuit board, and an IC. The main feature of the
optical module according to the embodiment is a connection
relationship between the first optical subassembly and the first
flexible printed circuit board, and a connection relationship
between the second optical subassembly and the second flexible
printed circuit board.
[0050] FIG. 6 is a diagram illustrating a connection relationship
between the two LD modules 31A and 31B and the two flexible printed
circuit boards 45A and 45B according to the embodiment. Here, the
upper LD module 31A corresponds to the first optical subassembly,
and the lower LD module 31B corresponds to the second optical
subassembly. The LD module 31A and the LD module 31B are disposed
in a row in the y orientation so as to be in parallel with each
other. Here, the LD module 31A and the LD module 31B are disposed
in a row in order in the -y direction. The flexible printed circuit
board 45A connected to the LD module 31A corresponds to the first
flexible printed circuit board. The flexible printed circuit board
45B connected to the LD module 31B corresponds to the second
flexible printed circuit board.
[0051] The stem 35 of the LD module 31A includes one pair of lead
terminals 51A and 51B which are disposed in a row in order in the
+x direction (positive direction of the first orientation, the left
direction in FIG. 6). That is, the LD module 31A includes the one
pair of lead terminals 51A and 51B which are disposed on the end
surface of the LD module 31A. Here, the lead terminal 51A
corresponds to a first normal phase lead terminal. The lead
terminal 51B corresponds to a first reverse phase lead terminal.
The lead terminal 51A is electrically connected to a positive
electrode (anode) of the LD element 36A in the LD module 31A. The
lead terminal 51B is electrically connected to a negative electrode
(cathode) of the LD element 36A. The stem 35 of the LD module 31A
maintains a ground potential. The stem 35 has a connection surface
which is a flat surface facing the back surface L2 of the flexible
printed circuit board 45A.
[0052] The flexible printed circuit board 45A includes one pair of
strip conductors 61A and 61B, a ground conductor layer 62 (not
illustrated), and ground conductor patterns 63A and 63B. The strip
conductors 61A and 61B are disposed on the front surface L1 of the
flexible printed circuit board 45A so as to extend in parallel with
each other. The ground conductor layer 62 is disposed on the back
surface L2 (not illustrated) thereof. Here, the strip conductor 61A
corresponds to a first normal phase strip conductor connected to
the lead terminal 51A (conductor functioning as a strip line for
transmitting a normal phase signal to the positive electrode of the
LD element). The strip conductor 61B corresponds to a first reverse
phase strip conductor connected to the lead terminal 51B (conductor
functioning as a strip line for transmitting a reverse phase signal
to the negative electrode of the LD element). The one pair of strip
conductors 61A and 61B are disposed at a connection portion with
the end surface of the LD module 31A in a row in order in the +x
direction, and extend in parallel with each other in the +y
direction (positive direction of the second orientation). Each of
the one pair of strip conductors 61A and 61B has an opening at one
end. The opening is provided for penetrating the one pair of lead
terminals 51A and 51B. The ground conductor patterns 63A and 63B
are disposed at both edges of the front surface L1 of the flexible
printed circuit board 45A, respectively. A plurality of
through-holes 64 are provided in order to penetrate the ground
conductor patterns 63A and 63B disposed on the front surface L1 and
the ground conductor layer 62 disposed on the back surface L2,
respectively.
[0053] The flexible printed circuit board 45A is disposed in the LD
module 31 such that the one pair of lead terminals 51A and 51B on
the end surface of the LD module 31A (on the connection surface of
the stem 35) penetrate the openings of the one pair of strip
conductors 61A and 61B on the flexible printed circuit board 45A.
The one pair of lead terminals 51A and 51B are electrically
connected to the one pair of strip conductors 61A and 61B via
solders 55A, respectively. The connection surface of the stem 35 is
electrically connected to each of the ground conductor patterns 63A
and 63B of the flexible printed circuit board 45A via solders 55B.
(At least some of) The plurality of through-holes 64 are filled
with the solders 55B. Thus, the ground conductor patterns 63A and
63B are also electrically connected to the ground conductor layer
62 disposed on the back surface. A coverlay 65 is disposed on the
front surface L1 of the flexible printed circuit board 45A. The
coverlay 65 covers the one pair of strip conductors 61A and 61B
except for a connection region with the pair of lead terminals 51A
and 51B and an arrangement region of the solders 55B for
electrically connecting the main body of the stem 35 to the two
ground conductor patterns 63A and 63B. Similarly, the coverlay 65
(not illustrated) is disposed on the back surface L2 of the
flexible printed circuit board 45A. The coverlay 65 covers the
ground conductor layer 62 (not illustrated) except for a region
which faces the connection surface 35A of the stem 35.
[0054] Similar to the LD module 31A, the stem 35 of the LD module
31B includes one pair of lead terminals 51A and 51B which are
disposed in a row in order in the +x direction. Here, the lead
terminal 51A corresponds to the second normal phase lead terminal.
The lead terminal 51B corresponds to the second reverse phase lead
terminal. That is, the stem 35 of the LD module 31B has the same
configuration as that of the stem 35 of the LD module 31A, and
coincides with an object obtained by translationally moving the
stem 35 of the LD module 31A in the -y direction. The LD element
36B mounted therein is different from the LD element 36A in a point
of a structure which causes an optical signal having a wavelength
different from that of the LD element 36A to be emitted. However,
regarding other components, the LD module 31B coincides with an
object obtained by translationally moving the LD module 31A in the
-y direction. That is, in the optical module according to the
embodiment, the first optical subassembly and the second optical
subassembly have a common structure except for the light conversion
element mounted therein. Thus, it is not required to design,
manufacture, and prepare two kinds of optical subassemblies, and
reduction of manufacturing cost is realized. If the same designed
components can be used as components (TO-CAN package: PKG) other
than the LD element in the LD module (TO-CAN TOSA), the quantity of
the PKG is four per one optical module. Thus, reduction of price
occurring by the quantity effect is also achieved. According to the
examination of the inventors, in order to perform division into
four LD modules, an outer diameter of (a stem) of the LD module is
desirably equal to or smaller than 4 mm and further desirably equal
to or smaller than 3.8 mm.
[0055] In the stem 35 according to the embodiment, the one pair of
lead terminals 51A and 51B are disposed on the center line of the
connection surface of the stem 35 in the y orientation. As
described above, the one pair of lead terminals disposed on the end
surface of the optical subassembly according to the embodiment are
desirably disposed in the vicinity of the center line of the end
surface of the optical subassembly in the y orientation. It is
desirable that the one pair of lead terminals are disposed within a
region of .+-.10% from the center in the y orientation with respect
to the outer diameter (length from one edge to the other edge on
the center line in the x orientation) of the end surface. It is
more desirable that the one pair of lead terminals are disposed
within a region of .+-.5% from the center.
[0056] The lead terminals included in the stem 35 are not limited
only to the one pair of lead terminals 51A and 51B according to the
embodiment, and may include another lead terminal. For example, the
lead terminals may further include a lead terminal connected to an
output electric signal of a monitor PD element which is disposed
for detecting an optical output of the LD element. Regarding the
ground potential, from a viewpoint of reduction in size of an
optical subassembly, as in the embodiment, it is desirable that a
ground conductor region of the flexible printed circuit board and
the main body of the stem are directly brazed. However, it is not
limited thereto. A lead ground terminal connected at the ground
potential of the optical subassembly may be further included. In
this case, it is necessary that the stem 35 is disposed to be
reversed in the y orientation for the LD modules 31A and 31B.
[0057] The flexible printed circuit board 45B includes one pair of
strip conductors 61A and 61B which are disposed on the front
surface L1 thereof, a ground conductor layer 62 (not illustrated)
disposed on the back surface L2 thereof, and ground conductor
patterns 63A and 63B. Here, the strip conductor 61A corresponds to
the second normal phase strip conductor. The strip conductor 61B
corresponds to the second reverse phase strip conductor. The one
pair of strip conductors 61A and 61B are disposed at a connection
portion with the end surface of the LD module 31B in a row in order
in the +x direction, and extend in parallel with each other in the
-y direction. That is, the one pair of strip conductors 61A and 61B
of the flexible printed circuit board 45A and the one pair of strip
conductors 61A and 61B of the flexible printed circuit board 45B
are arranged in order in the +x direction. However, the one pair of
strip conductors 61A and 61B of the flexible printed circuit board
45A extend in the +y direction, and the one pair of strip
conductors 61A and 61B of the flexible printed circuit board 45B
extend in the -y direction. That is, a direction in which the strip
conductors 61A and 61B of the flexible printed circuit board 45A
extend is opposite to a direction in which the strip conductors 61A
and 61B of the flexible printed circuit board 45B extend. As
illustrated in FIG. 6, if the center line between the LD module 31A
and the LD module 31B is set to be a straight line X1, the flexible
printed circuit board 45B coincides with an object obtained by
symmetrically moving the flexible printed circuit board 45A in line
symmetry based on the straight line X1. If the flexible printed
circuit board 45A and the flexible printed circuit board 45B
overlap each other so as to cause outer edges to coincide with each
other (if the flexible printed circuit board 45A is symmetrically
moved in point symmetry based on a center O on the straight line
X1), the flexible printed circuit board 45A and the flexible
printed circuit board 45B completely coincide with each other and
have the common structure. Disposition of the one pair of strip
conductors 61A and 61B is performed so as to be reverse to each
other. That is, the flexible printed circuit board 45A and the
flexible printed circuit board 45B may be the same product. In a
case where one of the one pair of strip conductors functions as the
first normal phase strip conductor in the flexible printed circuit
board 45A, this functions as the second reverse phase strip
conductor in the flexible printed circuit board 45B. In a case
where the other of the one pair of strip conductors functions as
the first reverse phase strip conductor in the first flexible
printed circuit board, this functions as the second normal phase
strip conductor in the second flexible printed circuit board. In
the optical module according to the embodiment, the first flexible
printed circuit board and the second flexible printed circuit board
have the common structure. Thus, it is not required to design,
manufacture, and prepare two kinds of flexible printed circuit
boards, and reduction of manufacturing cost is realized.
[0058] One end of each of the one pair of strip conductors 61A and
61B of the flexible printed circuit board 45A (or 45B) is connected
to each of the one pair of lead terminals 51A and 51B of the LD
module 31A (or 31B). The other end thereof is electrically
connected to each of one pair of board signal terminals 71A and 71B
of the printed circuit board 21. As illustrated in FIG. 5B, the
printed circuit board 21 according to the embodiment has the first
surface (upper surface) S1 and the second surface (lower surface)
S2. A normal orientation of the first surface S1 and a normal
orientation of the second surface S2 are directed in the y
orientation together. Here, the first surface S1 rather than the
second surface S2 is positioned on the positive side (upper part in
FIG. 5B) of the y orientation. As illustrated in FIG. 5B, the
flexible printed circuit board 45A is connected so as to cause the
front surface L1 thereof to face the first surface S1. The flexible
printed circuit board 45B is connected so as to cause the front
surface L1 thereof to face the second surface S2.
[0059] FIG. 7A is a plan view illustrating an end portion of the
flexible printed circuit board 45A (first flexible printed circuit
board) according to the embodiment. FIG. 7B is a bottom view
illustrating the end portion of the flexible printed circuit board
45A (first flexible printed circuit board) according to the
embodiment. That is, FIG. 7A illustrates the front surface L1 of
the flexible printed circuit board 45A, and FIG. 7B illustrates the
back surface L2 of the flexible printed circuit board 45A. FIGS. 7A
and 7B illustrate the +x direction (first orientation) and a +z
direction. A z orientation is perpendicular to both the x
orientation (first orientation) and the y orientation (second
orientation). The one pair of strip conductors 61A and 61B disposed
on the front surface L1 of the flexible printed circuit board 45A
extend in parallel with each other, from one end (opening). The one
pair of strip conductors 61A and 61B extend in parallel with each
other in the +z direction and reach the other end, while each of
the strip conductors 61A and 61B maintains a common predetermined
width (first width). The one pair of strip conductors 61A and 61B
extend in parallel with each other in the +z direction and reach
the other end, while the strip conductors 61A and 61B are separate
from each other with maintaining a predetermined gap (first gap).
The one pair of strip conductors 61A and 61B include one pair of
front-surface signal terminals 66A and 66B at the other end. At end
portions of the one pair of strip conductors 61A and 61B on the
other end side, the width of each of the one pair of strip
conductors 61A and 61B gradually becomes wider than the
predetermined width (first width), and then becomes equal to a
width (second width) of the one pair of front-surface signal
terminals 66A and 66B. Each of the one pair of strip conductors 61A
and 61B reaches the other end while maintaining this width. At the
end portions thereof on the other end side, the gap between the one
pair of strip conductors 61A and 61B gradually becomes wider than
the predetermined gap (first gap), and then becomes equal to a gap
(second gap) between the one pair of front-surface signal terminals
66A and 66B. The strip conductors 61A and 61B reach the other end
while maintaining this gap. Front-surface ground terminals 67A and
67B are disposed on the front surface of the flexible printed
circuit board 45A, on an outside of each of the one pair of
front-surface signal terminals 66A and 66B. The shape of the one
pair of strip conductors 61A and 61B includes the shape of the one
pair of front-surface signal terminals 66A and 66B and an adequate
shape may be selected.
[0060] As illustrated in FIG. 7B, one pair of back-surface signal
terminals 68A and 68B are disposed on the back surface of the
flexible printed circuit board 45A so as to overlap the one pair of
the front-surface signal terminals 66A and 66B in plan view. The
ground conductor layer 62 includes one pair of back-surface ground
terminals 69A and 69B at the other end. The one pair of
back-surface ground terminals 69A and 69B are disposed to overlap
the one pair of front-surface ground terminals 67A and 67B in plan
view. A plurality of through-holes 70 are provided between the one
pair of front-surface signal terminals 66A and 66B and the one pair
of back-surface signal terminals 68A and 68B. Similarly, a
plurality of through-holes 70 are provided between the
front-surface ground terminals 67A and 67B and the back-surface
ground terminals 69A and 69B. Practically, the coverlays 65 are
disposed on the front surface L1 and the back surface L2,
respectively, of the flexible printed circuit board 45A except for
a region in which a terminal group (front-surface signal terminal,
front-surface ground terminal, back-surface signal terminal, and
back-surface ground terminal) is disposed. However, for simple
descriptions, the illustration of the coverlays 65 are omitted in
FIGS. 7A and 7B.
[0061] FIG. 8 is a plan view illustrating an end portion of the
printed circuit board 21 according to the embodiment. FIG. 8
illustrates the first surface S1 of the printed circuit board 21.
The printed circuit board 21 includes the one pair of board signal
terminals 71A and 71B and one pair of board ground terminals 72A
and 72B which are disposed on the first surface S1. The printed
circuit board 21 is disposed to face the LD modules 31A, 31B, 31C,
and 31D in the z orientation. The one pair of board signal
terminals 71A and 71B disposed at an end portion are arranged in
order in the +x direction. Here, the board signal terminal 71A
corresponds to the first normal phase board terminal connected to
the first normal phase strip conductor. The board signal terminal
71B corresponds to the first reverse phase board terminal connected
to the first reverse phase strip conductor. The one pair of
front-surface signal terminals 66A and 66B of the flexible printed
circuit board 45A are disposed to face the one pair of board signal
terminals 71A and 71B disposed on the first surface S1 of the
printed circuit board 21. The one pair of front-surface ground
terminals 67A and 67B are disposed to face the one pair of board
ground terminals 72A and 72B disposed on the first surface S1. A
solder is injected from the back surface side of the flexible
printed circuit board 45A and thus electric connection is secured.
Thus, the one pair of front-surface signal terminals 66A and 66B
are electrically connected to the one pair of board signal
terminals 71A and 71B, respectively. The back-surface ground
terminals 69A and 69B are electrically connected to the board
ground terminals 72A and 72B.
[0062] The printed circuit board 21 includes one pair of strip
conductors 73A and 73B on the first surface S1, and includes the
one pair of board signal terminals 71A and 71B at one ends of the
one pair of strip conductors 73A and 73B. Here, the strip conductor
73A corresponds to a first positive-phase board strip conductor and
the strip conductor 73B corresponds to a first reverse-phase board
strip conductor. As illustrated in FIG. 8, the width of each of the
one pair of strip conductors 73A and 73B gradually becomes narrower
than the width (second width) of the one pair of board signal
terminals 71A and 71B, and then becomes equal to a predetermined
width (third width). Each of the one pair of strip conductors 73A
and 73B extends in the +z direction (lower direction illustrated in
FIG. 8) while maintaining this width. The one pair of strip
conductors 73A and 73B are connected to one pair of first IC signal
terminals 91A and 91B of the IC 48. The one pair of strip
conductors 73A and 73B extend with maintaining a gap (second gap)
between the one pair of board signal terminals 71A and 71B. That
is, the one pair of strip conductors 73A and 73B extend in parallel
with each other in the +z direction. The shape of the one pair of
strip conductors 73A and 73B includes the shape of the one pair of
board signal terminals 71A and 71B and an adequate shape may be
selected.
[0063] The printed circuit board 21 has a multilayer structure in
which a plurality of metal layers are stacked. A dielectric layer
is disposed between the metal layers which are adjacent to each
other. When viewed from the first surface S1 side, among the metal
layers in the multilayer structure, the one pair of strip
conductors 73A and 73B and the board ground terminals 72A and 72B
are disposed in the first metal layer. A ground conductor layer 74A
(not illustrated) is disposed in the second metal layer. A
plurality of through-holes 70 are provided between the board ground
terminals 72A and 72B and the ground conductor layer 74A. When the
flexible printed circuit board 45A and the printed circuit board 21
are connected to each other by solders, the solders are injected
into the plurality of the through-holes 70 of the printed circuit
board 21, and thus the board ground terminals 72A and 72B are
electrically connected to the ground conductor layer 74A.
[0064] A micro-strip line type first differential transmission line
is configured by including the one pair of strip conductors 73A and
73B and the ground conductor layer 74A. Here, the one pair of strip
conductors 73A and 73B ideally extend in the -z direction, and then
are connected to the one pair of first IC signal terminals 91A and
91B of the IC 48. The one pair of strip conductors 73A and 73B
include a portion which is bent if necessary, in practice. The one
pair of strip conductors 73A and 73B are connected to the one pair
of first IC signal terminals 91A and 91B of the IC 48.
[0065] The end portion of the flexible printed circuit board 45B
(second flexible printed circuit board) according to the embodiment
has a structure which is common with that of the flexible printed
circuit board 45A illustrated in FIGS. 7A and 7B. However, as
described above, disposition of the one pair of strip conductors
61A and 61B is performed so as to be reverse to each other. Since
the flexible printed circuit board 45B is connected so as to cause
the front surface L1 to face the second surface S2 of the printed
circuit board 21, the +x direction in the front surface L1 of the
flexible printed circuit board 45B is reverse to the +x direction
in the front surface L1 of the flexible printed circuit board 45A
illustrated in FIG. 7A. The one pair of strip conductors 61A and
61B provided on the front surface L1 of the flexible printed
circuit board 45B are arranged in a direction reverse to the one
pair of strip conductors 61A and 61B illustrated in FIG. 7A, and
are arranged in order in the +x direction (toward the left side
from the right side in FIG. 7A). Similarly, the one pair of
front-surface signal terminals 66A and 66B and the front-surface
ground terminals 67A and 67B are arranged in a direction reverse to
that in a case illustrated in FIG. 7A. The front-surface ground
terminals 67A and 67B are maintained at the ground potential. Thus,
there is no need for distinguishing the front-surface ground
terminals 67A and 67B from each other. However, for simple
descriptions, it is assumed that the front-surface ground terminals
67A and 67B are arranged in a reverse direction.
[0066] Similar to the front surface L1, regarding the back surface
L2 of the flexible printed circuit board 45B (second flexible
printed circuit board) according to the embodiment, the +x
direction in the back surface L2 of the flexible printed circuit
board 45B is reverse to the +x direction in the back surface L2 of
the flexible printed circuit board 45A illustrated in FIG. 7B. The
one pair of back-surface signal terminals 68A and 68B and the
back-surface ground terminals 69A and 69B are arranged in a
direction reverse to that in a case illustrated in FIG. 7B.
[0067] The above descriptions are similarly applied to the second
surface S2 of the printed circuit board 21 according to the
embodiment. The +x direction in the second surface S2 of the
printed circuit board 21 is reverse to the +x direction in the
first surface S1 illustrated in FIG. 8. One pair of strip
conductors 75A and 75B provided on the second surface S2 of the
printed circuit board 21 are arranged in a direction reverse to the
one pair of strip conductors 73A and 73B in the first surface S1
illustrated in FIG. 8, and are arranged in order in the +x
direction in FIG. 9 (toward the right side from the left side in
FIG. 8). Here, the strip conductor 75A corresponds to a second
normal phase board strip conductor. The strip conductor 75B
corresponds to a second reverse phase board strip conductor.
Similarly, the one pair of strip conductors 75A and 75B include the
one pair of board signal terminals 71A and 71B at one end. However,
the one pair of board signal terminals 71A and 71B and the board
ground terminals 72A and 72B are arranged in a direction reverse to
that in a case illustrated in FIG. 8.
[0068] When viewed from the second surface S2 side, among the metal
layers in the multilayer structure of the printed circuit board 21,
the one pair of strip conductors 75A and 75B and the board ground
terminals 72A and 72B are disposed in the first metal layer. A
ground conductor layer 74B (not illustrated) is disposed in the
second metal layer. The one pair of board ground terminals 72A and
72B are electrically connected to the ground conductor layer 74B
via the plurality of through-holes 70 by the solder. A micro-strip
line type second differential transmission line is configured on
the second surface S2 side of the printed circuit board 21 by
including the one pair of strip conductors 75A and 75B and the
ground conductor layer 74B. Here, the one pair of strip conductors
75A and 75B ideally extend in the +z direction, and then are
connected to one pair of second IC signal terminals 92A and 92B of
the IC 48. The IC 48 is mounted on the first surface S1 of the
printed circuit board 21. In this case, since the IC 48 is
electrically connected to the LD module 31B, the second
differential transmission line extends on the second surface from
the one pair of board signal terminals 71A and 71B (and the ground
conductor layer 74B) (second surface differential transmission
line). The second differential transmission line extends from the
second surface to the first surface in a stacking direction (+y
direction) (stacking direction differential transmission line), and
then extends on the first surface (first surface differential
transmission line), and thus is connected to the one pair of second
IC signal terminals 92A and 92B. Details thereof will be described
later.
[0069] In the embodiment, it is noted that xyz coordinates are
defined with respect to a space. Thus, for example, when an
observer views the optical module 2 from the +y direction (upper
part of the printed circuit board 21), an order in which the one
pair of lead terminals 51A and 51B in each of the LD modules 31A
and 31B are arranged is directed in the +x direction. At a
connection portion with the LD modules 31A and 31B, an order in
which the one pair of strip conductors 61A and 61B in the flexible
printed circuit boards 45A and 45B are arranged is directed in the
+x direction. An order in which the one pair of strip conductors
61A and 61B of the flexible printed circuit boards 45A and 45B at a
connection portion with the printed circuit board 21 are arranged
(that is, order of arranging the pair of front-surface signal
terminals 66A and 66B) is also directed in the +x direction. An
order in which the one pair of board signal terminals 71A and 71B
disposed on each of the first surface S1 and the second surface S2
of the printed circuit board 21 are arranged is also directed in
the +x direction. With such a configuration, the LD modules 31A and
31B have the common configuration (other than the LD element).
Thus, it is possible to prepare two LD modules 31A and 31B at low
cost. Similarly, the flexible printed circuit boards 45A and 45B
have the common configuration, and thus it is possible to prepare
two flexible printed circuit boards 45A and 45B at low cost.
Regardless of the order, in plan view, an order of a plurality of
pairs of strip conductors disposed on the printed circuit board 21
for a normal phase can be the same as an order of a plurality of
pairs of strip conductors disposed on the printed circuit board 21
for a reverse phase. As with the second differential transmission
line, even in a case where the strip conductor is configured from
the second surface to the first surface, the printed circuit board
21 can be configured without a need for the special structure, for
example, in which an arrangement order is inverted by causing one
pair of strip conductors to intersect three-dimensionally.
[0070] FIG. 9 is a plan view illustrating the printed circuit board
21 according to the embodiment. FIG. 10 is a cross-sectional view
illustrating the printed circuit board 21 according to the
embodiment. FIG. 9 illustrates a portion of the first surface S1 of
the printed circuit board 21. FIG. 10 illustrates a cross-section
taken along line X-X illustrated in FIG. 9. As described above, the
flexible printed circuit boards 45A and 45D which are respectively
connected to the LD modules 31A and 31D at the upper stage are
connected to the first surface S1 of the printed circuit board 21.
The flexible printed circuit boards 45B and 45C which are
respectively connected to the LD modules 31B and 31C at the lower
stage are connected to the second surface S2 of the printed circuit
board 21. Four connection terminals (board ground terminal 72A,
board signal terminal 71A, board signal terminal 71B, and board
ground terminal 72B) for CH1 (LD module 31A) and four connection
terminals for CH4 (LD module 31D) are arranged on the first surface
S1 illustrated in FIG. 9, in order in the +x direction. Similarly,
four connection terminals for CH2 (LD module 31B) and four
connection terminals for CH3 (LD module 31C) are arranged on the
second surface S2 in order in the +x direction. In plan view, the
four connection terminals for CH1 overlap the four connection
terminals for CH2, respectively. The four connection terminals for
CH4 overlap the four connection terminals for CH3,
respectively.
[0071] The IC 48 has a rectangular shape. The one pair of first IC
signal terminals 91A and 91B for CH1, the one pair of second IC
signal terminals 92A and 92B for CH2, one pair of third IC signal
terminals 93A and 93B for CH3, and one pair of fourth IC signal
terminals 94A and 94B for CH4 are arranged on one side of the
rectangular shape, which extends in the x orientation and faces the
connection terminals for CH1 and CH4 on the first surface S1, in
order in the +x direction. Here, the first IC signal terminal 91A
for CH1 corresponds to the first normal phase IC terminal. The
first IC signal terminal 91B for CH1 corresponds to the first
reverse phase IC terminal. Similarly, the second IC signal terminal
92A for CH2 corresponds to the second normal phase IC terminal, and
the second IC signal terminal 92B for CH2 corresponds to the second
reverse phase IC terminal. The above descriptions are similarly
applied to cases of CH3 and CH4.
[0072] As described above, the one pair of strip conductors 73A and
73B extend from the one pair of board signal terminals 71A and 71B
for CH1, and are respectively connected to the one pair of first IC
signal terminals 91A and 91B (for CH1). The first differential
transmission line is configured by including the one pair of the
strip conductors 73A and 73B and the ground conductor layer 74A.
The second differential transmission line includes the one pair of
strip conductors 75A and 75B disposed on the second surface S2, one
pair of via-holes 76A and 76B, one pair of strip conductors 77A and
77B disposed on the first surface S1, the ground conductor layer
74B, a plurality of ground via-holes 78 (not illustrated), and the
ground conductor layer 74A. The second differential transmission
line is connected to each of the one pair of second IC signal
terminals 92A and 92B (for CH2). Each of the one pair of strip
conductors 75A and 75B has a land portion at one end thereof.
Similarly, each of the one pair of strip conductors 77A and 77B has
a land portion at one end thereof. Each of the one pair of
via-holes 76A and 76B electrically connects each of the land
portions of the one pair of strip conductors 75A and 75B and each
of the land portions of the one pair of strip conductors 77A and
77B. The plurality of ground via-holes 78 electrically connect the
ground conductor layer 74B and the ground conductor layer 74A.
[0073] As described above, the second differential transmission
line includes the second-surface differential transmission line,
the stacking-direction differential transmission line, and the
first-surface differential transmission line. The second-surface
differential transmission line includes the one pair of strip
conductors 75A and 75B and the ground conductor layer 74B. The
stacking-direction differential transmission line includes the one
pair of via-holes 76A and 76B, and the plurality of ground
via-holes 78. The first-surface differential transmission line
includes the one pair of strip conductors 77A and 77B and the
ground conductor layer 74. The one pair of strip conductors 77A and
77B extend so as to be respectively connected to the one pair of
second IC signal terminals 92A and 92B for (CH2).
[0074] The transmission line (third differential transmission line)
for CH3 has the same structure as that of the transmission line for
CH2. The transmission line (fourth differential transmission line)
for CH4 has the same structure as that of the transmission line for
CH1. As illustrated in FIG. 10, similar to the flexible printed
circuit boards 45A and 45B, the coverlays 65 are disposed on the
first surface S1 and the second surface S2 of the printed circuit
board 21, respectively. However, for simple descriptions, the
illustration of the coverlay 65 is omitted in FIG. 9. As
illustrated in FIG. 10, the flexible printed circuit board 21 has a
multilayer structure. However, a dielectric layer 80 is disposed
between metal layers which are adjacent to each other.
[0075] In the embodiment, the first IC signal terminals 91A and
91B, the second IC signal terminals 92A and 92B, the third IC
signal terminals 93A and 93B, and the fourth IC signal terminals
94A and 94B which are disposed in the IC 48 are disposed in order
in the +x direction. By arranging the differential transmission
line (the strip conductor of the differential transmission line) to
be close to a straight line as much as possible, it is possible to
realize space saving. Accordingly, as in the embodiment, it is
desirable that the IC signal terminals are disposed in a row in
order in the +x direction. However, it is not limited thereto. For
example, the IC signal terminals may be disposed in a row in order
in the z orientation of the IC 48. In this case, it is assumed that
the IC signal terminals are disposed in order in a positive
direction of a third orientation. In the embodiment, the positive
direction of the third orientation corresponds to the positive
direction of the first orientation.
[0076] The optical module according to the embodiment is best in a
case where the outer diameter of an optical subassembly is equal to
or smaller than 4.0 mm. In the embodiment, the IC 48 is a driving
circuit which can control the four LD modules 31A, 31B, 31C, and
31D. In a case where the IC is mounted on the first surface S1 of
the printed circuit board 21, the LD modules 31A and 31D at the
upper stage are connected to the connection terminal on the first
surface S1 via the flexible printed circuit boards 45A and 45D. On
the contrary, the LD modules 31B and 31C at the lower stage are
connected to the connection terminal on the second surface S2 via
the flexible printed circuit boards 45B and 45C. In this case, the
differential transmission line corresponds to the
stacking-direction differential transmission line, and is required
to move from the second surface S2 to the first surface S1.
Generally, plural pairs of IC signal terminals disposed in the IC
48 are repetitively arranged in a row in an order of a normal
phase, a reverse phase, a normal phase, and a reverse phase. Even
in the differential transmission line which moves from the second
surface S2 to the first surface S1, it is important to maintain an
arrangement order of a normal phase and a reverse phase of one pair
of strip conductors of each channel. In the embodiment, a direction
in which the first flexible printed circuit board extends is
opposite to a direction in which the second flexible printed
circuit board extends. Thus, in plan view, it is possible to easily
maintain an arrangement order of the normal phase and the reverse
phase.
[0077] Non-conformity of characteristic impedance easily occurs at
a connection portion between the flexible printed circuit board and
the printed circuit board. In order to perform more conforming of
the characteristic impedance, structural optimization using an
electromagnetic field simulation is required. For example, in a
case where the characteristic impedance in a case where the surface
(front surface or back surface) of the flexible printed circuit
board is connected to the first surface of the printed circuit
board is different from the characteristic impedance in a case
where the surface (front surface or back surface) of the flexible
printed circuit board is connected to the second surface of the
printed circuit board, inductance or capacitance restricted at the
connection portion also varies. Thus, the configuration (shape of
the one pair of strip conductors) of the differential transmission
line disposed on each of the first surface and the second surface
of the printed circuit board is changed. Accordingly, a long time
takes for design and manufacturing cost is increased. In the
optical module according to the embodiment, a mounting direction of
the flexible printed circuit board based on the printed circuit
board is not changed between cases of the first surface and the
second surface, and an arrangement order of the normal phase and
the reverse phase in plan view may be set. Thus, it is possible to
reduce the manufacturing cost. In this specification, for
convenient descriptions, the terms called as the normal phase and
the reverse phase are used. However, even though the arrangement of
the normal phase and the reverse phase in the embodiment is reverse
to each other, the effect of the present invention is obtained. In
this case, a direction set as the +x direction is inverted.
Second Embodiment
[0078] FIG. 11 is a cross-sectional view illustrating an optical
module 2 according to a second embodiment of the present invention.
FIG. 12 is a diagram illustrating a connection relationship between
two LD modules 31A and 31B and two flexible printed circuit boards
45A and 45B according to the embodiment. The optical module 2
according to the embodiment has the same structure as that in the
first embodiment except that the connection relationship of the two
flexible printed circuit boards 45A and 45B with the LD modules 31A
and 31B or the connection relationship with the printed circuit
board 21 are different from those in the first embodiment.
[0079] As illustrated in FIG. 12, one pair of strip conductors 61A
and 61B in the flexible printed circuit board 45A are disposed in a
row in order in the +x direction and extend in parallel with each
other in a lower direction in FIG. 12, at a connection portion with
the end surface of the LD module 31A. On the contrary, one pair of
strip conductors 61A and 61B in the flexible printed circuit board
45B are disposed in a row in order in the +x direction and extend
in parallel with each other in an upper direction in FIG. 12, at a
connection portion with the end surface of the LD module 31B. In
the specification, regarding the direction of the second
orientation (y orientation), since a direction in which the one
pair of strip conductors 61A, 61B of the first flexible printed
circuit board extend is defined to be the positive direction, as
illustrated in FIG. 12, in the second embodiment, the direction of
the y orientation is opposite to a direction of the y orientation
in the first embodiment. That is, the one pair of strip conductors
61A and 61B of the flexible printed circuit board 45A extend in the
+y direction, at a connection portion with the end surface of the
LD module 31A. The one pair of strip conductors 61A and 61B of the
flexible printed circuit board 45B extend in the -y direction, at
the connection portion with the end surface of the LD module 31B.
However, as described above, since the direction of the +y
direction is opposite to that in the first embodiment, both thereof
extend in a direction of being closer to each other.
[0080] In the embodiment, the first surface S1 of the printed
circuit board 21 rather than the second surface S2 is positioned on
the negative side (upper part in FIG. 11) of the y orientation. The
LD module 31A and the LD module 31B are disposed in a row in order
in the +y direction. As illustrated in FIG. 11, the flexible
printed circuit board 45A is connected to the LD module 31A so as
to cause the end surface of the LD module 31A to face the back
surface L2 of the flexible printed circuit board 45A. The flexible
printed circuit board 45A is connected to the printed circuit board
21 so as to cause the back surface L2 of the flexible printed
circuit board 45A to face the first surface S1 of the printed
circuit board 21. On the contrary, the flexible printed circuit
board 45B is connected to the LD module 31B so as to cause the end
surface of the LD module 31B to face the back surface L2 of the
flexible printed circuit board 45B. The flexible printed circuit
board 45A is connected to the printed circuit board 21 so as to
cause the back surface L2 of the flexible printed circuit board 45B
to face the first surface S1 of the printed circuit board 21.
[0081] The flexible printed circuit boards 45A and 45B extend in a
direction of being close to each other, from portions which are
respectively connected to the LD modules 31A and 31B. However, the
flexible printed circuit boards 45A and 45B are bent to move to the
printed circuit board 21 together so as to face the back surfaces
L2 thereof. The back surfaces L2 on which ground conductor layer 42
is disposed face each other, and thus crosstalk occurring between
the flexible printed circuit boards 45A and 45B which are disposed
to be adjacent to each other is reduced. In order to realize high
density mounting, LD modules are disposed to be adjacent to each
other at a short distance, and thus crosstalk would occur between
the LD modules. However, in the optical module 2 according to this
embodiment, it is possible to exhibit an effect similar to that of
the optical module 2 according to the first embodiment and to
reduce the crosstalk.
[0082] In the embodiment, the flexible printed circuit board 45A is
connected to the printed circuit board 21 so as to cause the back
surface L2 of the flexible printed circuit board 45A to face the
first surface S1 of the printed circuit board 21. However, the
flexible printed circuit board 45A according to the embodiment has
the same structure as that of the flexible printed circuit board
45A according to the first embodiment illustrated in FIGS. 7A and
7B. In other words, in both the first embodiment and the second
embodiment, it is possible to use the flexible printed circuit
boards 45A and 45B having the same structure. In this embodiment,
since the back surface L2 of the flexible printed circuit board 45A
faces the first surface S1 of the printed circuit board 21, the one
pair of back-surface signal terminals 68A and 68B illustrated in
FIG. 7B are disposed to overlap the one pair of board signal
terminals 71A and 71B illustrated in FIG. 8. The back-surface
ground terminals 69A and 69B illustrated in FIG. 7B overlap the
board ground terminals 72A and 72B illustrated in FIG. 8. The
solder is injected through the one pair of front-surface signal
terminals 66A and 66B and the front-surface ground terminals 67A
and 67B illustrated in FIG. 7A, and thus an electrical connection
is secured.
[0083] Even in this embodiment, similar to the first embodiment, an
order in which the one pair of lead terminals 51A and 51B in each
of the LD modules 31A and 31B are arranged is directed in the +x
direction. An order in which the one pair of strip conductors 61A
and 61B of the flexible printed circuit boards 45A and 45B at a
connection portion with the LD modules 31A and 31B are arranged is
also directed in the +x direction. An order in which the one pair
of strip conductors 61A and 61B of the flexible printed circuit
boards 45A and 45B at a connection portion with the printed circuit
board 21 are arranged (that is, order of arranging the pair of
front-surface signal terminals 66A and 66B) is also directed in the
+x direction. An order in which the one pair of board signal
terminals 71A and 71B disposed on each of the first surface S1 and
the second surface S2 of the printed circuit board 21 are arranged
is also directed in the +x direction.
[0084] Hitherto, the optical module, the optical transmission
equipment, and the optical transmission system according to the
embodiment of the present invention are described. The present
invention is not limited to the above embodiments, and can be
widely applied to an optical transmitter module and an optical
receiver module. In the embodiments, a case where the optical
subassembly is an LD module, that is, a case where the optical
subassembly includes a light-emitting element is described.
However, it is not limited thereto. The present invention can also
be applied in a case where the optical subassembly is a PD module,
that is, in a case where the optical subassembly includes a
light-receiving element.
[0085] In the embodiments, a case where the IC is mounted on the
first surface of the printed circuit board is described. However,
the IC may be mounted on the second surface by symmetry. In a case
where the IC is mounted on the second surface of the printed
circuit board, the first differential transmission line extends
from the first normal phase board terminal and the first reverse
phase board terminal on the first surface, extends from the first
surface to the second surface in the stacking direction, and then
extends on the second surface so as to be connected to the first
normal phase IC terminal and the first reverse phase IC terminal.
The second differential transmission line extends from the second
normal phase board terminal and the second reverse phase board
terminal on the second surface, and thus is connected to the second
normal phase IC terminal and the second reverse phase IC
terminal.
[0086] In the embodiment, the IC 48 for transmission and the IC 49
for receiving are mounted together on the first surface S1 of the
printed circuit board 21. However, it is not limited thereto. For
example, the IC 48 may be mounted on the first surface S1 and the
IC 49 may be mounted on the second surface S2. In this case, the
flexible printed circuit board 22B is connected to the second
surface S2.
[0087] In the embodiments, the first optical subassembly and the
second optical subassembly are disposed in a row in the second
orientation (vertical orientation). However, it is not limited
thereto. For example, even if the first optical subassembly and the
second optical subassembly are disposed in a row in the first
orientation (horizontal orientation), in a case where it is
necessary that the first optical subassembly and the second optical
subassembly are separately connected to the first surface and the
second surface, the present invention can be applied. In this
specification, "being directed in the first orientation" is not
limited to a case of being in parallel with the first orientation,
and includes a case of being disposed so as to be directed in the
first orientation.
[0088] While there have been described what are at present
considered to be certain embodiments of the invention, it will be
understood that various modifications may be made thereto, and it
is intended that the appended claims cover all such modifications
as fall within the true spirit and scope of the invention.
* * * * *